This invention relates to the improvement of an electronic musical instrument of the harmonic wave synthesizing type therein a fundamental wave (fundamental tone) and its harmonic components (harmonic overtones) corresponding to the tone pitch of a depressed key are produced, the fundamental wave and the harmonic components are respectively multiplied with corresponding coefficients, and the products are added together to form a musical tone.
According to one type of the harmonic wave synthesizing type electronic musical instrument, a musical tone is obtained by sequentially calculating the amplitude values at successive sampling points of a musical tone waveform according to the following equation ##EQU1## where q=1, 2, 3, . . . x.sub.0 (qR) . . . amplitude value at successive sampling point of the musical tone waveform
R . . . a value proportional to the frequency (tone pitch) of the musical tone to be produced (hereinafter termed a "frequency number") PA1 n . . . the order of the harmonics including the fundamental wave PA1 C.sub.n . . . amplitude coefficients of the harmonic components of respective orders (Fourier coefficient) PA1 N . . . number of the sampling points of the musical tone waveform PA1 W . . . number of the harmonics (overtones) involved in the amplitude calculation at successive sampling points W=N/2
n=1 means the fundamental wave (fundamental tone) PA2 n=2 means the second harmonic wave (the second harmonic overtone) PA2 n=3 means the third harmonic wave (the third harmonic overtone)
An electronic musical instrument of the harmonic synthesizing type is disclosed, for example, in U.S. Pat. No. 3,809,786 invented by Ralph Deutsch and issued on May 7, 1974.
According to such an electronic musical instrument of a harmonic wave synthesizing type, a frequency number R corresponding to the tone pitch of a depressed key is generated, the frequency number R is sequentially accumulated each time a timing signal t.sub.x for determining a computation time is generated to obtain an accumulated value qR that sequentially designates the sampling points (phase angles) of the musical tone waveform, and the accumulated value qR is sequentially accumulated at the timing of a clock pulse to obtain a further accumulated value nqR which is used to produce (read out from the table) the sinusoidal wave amplitude value sin .pi./W nqR of each harmonic wave at successive sampling points. Accordingly, in the musical tone generated in this manner, the frequencies (period) of respective harmonics (including the fundamental wave) have a relation of interger multiples (harmonic overtones), thus producing a harmonic musical tone.
In the musical tone generated by the conventional natural musical instruments, however, the frequencies of respective harmonics are not integer multiples of the frequency of the fundamental wave (the first harmonic), that is the musical tone is not precisely harmonic thus producing a tone rich in naturality.
With the prior art electronic musical instrument of the harmonic wave synchronizing type described above it has been difficult to generate non-harmonic musical tones. Although U.S. Pat. No. 3,888,153 discloses an electronic musical instrument of a harmonic wave synthesizing type that can produce non-harmonic musical tones, in this patent is it necessary to add a new value to the accumulated value as an overtone offset value so that the construction is complicated. Moreover, it is impossible to set the overtone offset values of respective orders (respective harmonics) to any desired values to obtain desired non-harmonic property (inharmonicity).
In electronic musical instruments, for the purpose of controlling the pitch of the generated musical tones for obtaining various effects, such pitch controls as vibrato, glide, portamento, etc. have been used.
However, in order to provide the pitch control for the prior art electronic musical instrument of the harmonic wave synthesizing type, it is necessary to multiply the frequency number R comprising about 15 bits with a signal for effecting the pitch control. Such multiplying operation not only complicates the circuit construction but also requires a long time for the multiplying operation.